Developing device and image forming apparatus including developer conveying member and toner concentration sensor

A developing device, comprising:

• a development container which includes a first conveying chamber and a second conveying chamber arranged parallel to each other and communicating with each other at opposite end portion sides thereof in longitudinal directions thereof, and which stores a two-component developer including a toner and a carrier;
• a first conveying member which is rotatably arranged in the first conveying chamber and which conveys, while stirring, the developer in the first conveying chamber in a first direction along the longitudinal direction of the first conveying chamber;
• a second conveying member which is rotatably arranged in the second conveying chamber and which conveys, while stirring, the developer in the second conveying chamber in a second direction along the longitudinal direction of the second conveying chamber, the second direction being opposite to the first direction;
• a developer supply port which is arranged in an upstream-side wall portion of the first conveying chamber in the first direction, and through which the developer is supplied to the first conveying chamber;
• a toner concentration sensor which is arranged at a wall portion of the first conveying chamber along the first direction, and which detects a toner concentration of the developer;
• and
• a developer carrier which is rotatably supported in the development container, and which carries thereon the developer in the second conveying chamber,
• wherein
• the first conveying member and the second conveying member each include
• a rotation shaft extending along a longitudinal direction of the development container, and
• a conveying blade formed on an outer circumferential portion of the rotation shaft, the first conveying member and the second conveying member being equal to each other in outer diameter and in shaft diameter, the outer diameter being 2.3 times the shaft diameter or more but 3.0 times the shaft diameter or less,
• the toner concentration sensor is a headless sensor and has a sensing surface embedded in an inner wall surface of the first conveying chamber,
• a center of the sensing surface of the toner concentration sensor is located in a region extending downstream, in the first direction, from a center of the first conveying chamber in the longitudinal direction of the first conveying chamber, for a length that is equal to or less than one fourth of an entire length of the first conveying chamber in the longitudinal direction thereof, and
• where D [mm] represents the shaft diameter of the first conveying member, L [mm] represents an axial length of the first conveying member, and K [mm] represents a distance of a center position of the sensing surface of the toner concentration sensor from a downstream end of the first conveying chamber in the first direction, formula (1) below is satisfied:
• 500[mm−1]<(L2×K)/D4<2500[mm−1] (1).